Connector terminal generally used in a connector is constituted of a metallic material including copper (Cu) or a copper (Cu) alloy, having tin (Sn) plated thereon, and has an electrical contact section which is brought into contact and conducted with a mating connector terminal by fitting to the mating connector terminal in a front section thereof and a conductor crimping section which is crimped to a conductor of an electric wire at a rear section thereof.
The reason for applying Sn plating to the surface of a terminal base material is that Sn is very soft, spontaneous oxide coating of Sn can easily be mechanically destroyed by contact load between terminals in fitting connector terminals to each other, newly-formed surfaces of Sn can be contacted to each other, and as a result, good contact performance (that is, low and stabilized contact resistance) can stably be maintained over a long period of time.
Where the Sn plated layer is not present, an oxide coating of a hard copper (or copper alloy) base material appears on the surface, and as a result, mechanical destruction of the surface layer at the time of fitting a terminal to the base material cannot be expected. Furthermore, because the oxide coating of copper has very high volume resistivity, contact resistance between terminals is apt to become high.
By the way, recently an aluminum electric wire begun to be used in place of a copper electric wire even in the field of electric wire harness for automobiles for the purpose of reduction in weight and improvement in recycle property. The aluminum electric wire is an electric wire having an aluminum-made or aluminum alloy-made conductor section.
In the case of using the aluminum electric wire, crimping of a terminal particularly becomes a problem.
In the case that the conductor crimping part of the connector terminal is crimped to an aluminum (or aluminum alloy) core of the aluminum electric wire, electrical resistance of the crimping connection part is apt to become high due to, for example, difference in springback properties and difference in coefficient of thermal expansion, between aluminum (or aluminum alloy) and copper (or copper alloy). For this reason, in the case of crimping a copper terminal to an aluminum electric wire, overcrimping stronger than the general crimping is performed in order to suppress electrical resistance low. The overcrimping is a manner of crimping in which compressibility is large as compared with the case of crimping a copper terminal to a copper electric wire, and is that, for example, conductor compressibility is 60% or less.
However, the case that overcrimping has been performed gives rise to the problem that the core of an electric wire is too compressed, and as a result, in the case of receiving tensile load in an axial direction, the electric wire becomes easy to be broken in the crimping section (that is, decrease in strength in crimping section).
In view of the above, for example, in a crimp structure shown in Patent Document 1, as shown in FIG. 7, difference in level for separating a front side part and a rear side part is provided on a conductor crimp section 212 of a connector terminal 200, a terminal is weakly crimped to an aluminum electric wire in a crimping section 212a at a rear side (that is, with conductor compressibility to the same extent as the case to a copper wire), and is strongly crimped to an aluminum electric wire in a crimping section 212b at a front side (that is, with large conductor compressibility). Thus, by performing the crimping in two stages, both electrical connection performance and mechanical connection performance are attempted to achieve. At the front side of the conductor crimping section 212, an electrical contact section 210 which is brought into contact and conducted with a mating connector terminal by fitting to the mating connector terminal is provided, and at the rear side of the conductor crimping section 212, a covering swage section 213 swaged to an insulating cover-attached section of an electric wire W.